Spark plug with auxiliary gap



K. scHwARTzwALDl-:R ETAL 2,717,438

Sept. 13, 1955 SPARK PLUG WITH AUXILIARY GAP Original Filed March 17,1945 :inventors 9 f W w z h rn w. Mw

,sr M MM KK m Zl/I I attorney United States Patent@ Mich.; lassignonbtosGeneraLMotorsv fCorporation, De-

txoit,r lvlich.,- ,ancorporatidnaof. DelawareOi'igaiiapplication-Marchin 1945;' Serinl'No.' 583,364.' Divided fandthis applichtin\AugustA-'25,' 1949, Serial No. 115,039 ff (c1. zafzsiz)This invention has to do with spark plugshavingan auxiliary=sparkI f gapincorporated-Liri fthe' center electrode.

'Iltis-application is-iiled-.ilnderRille'l47 'as a divisional.

application-Lof'Srial-No'. 583',364,-le"d-March 17, 1945, now PatentNo.' 2,505 ,150#issued Aprill25,` 1950.'

ableit to'functioniefectivelydong'after-it would otherwise ihave'ebeen eshortcircuitedfby fouling, -that' is by the accumulationflo carbonaand'otherfconducting combustion chamber A-products -ontthe lfiring endofthe plug formingV a conducting path between theelectrode's; ThisVactionis increased/byplacingthe auxiliary gap `as close as possi-Vble'fto-Lthesparkigapiofthe plug`because the distributedVvcapacityj'of"thefportion-ofthe center electrode between' th'twogapsistherebyireduced-'to a minimum Aproducing fafsteepjwave-fr'ontatthe'sparkgapgso'that there is insuicient time forAleakageof'fcurrent through'the path produced by fouling topreventthe-spark =from jumpingthe gap.

An object rofatheepresentinvention -isf-toprovide an auxiliary gap of.durable constructionthatmay be readily incorporated in the centerelectrode of a spark plug and willfopevrateA ati substantially constantvoltage throughthe lifel'of the plugt- Another 'object ofthe/inventionfis-the provision of a simple and practical center electrodeconstruction embodying an auxiliary spark gap.

In the drawings:

Figure 1 is a vertical sectional View through one form of spark plugembodying my invention.

Figure 2 is a vertical sectional view through a modified form of sparkplug embodying my invention.

In Figure 1, indicates the lower part of the metal shell of the sparkplug having secured to its lower end the side electrodes indicated at12. Within the shell is the insulator 14, preferably of aluminum oxidecomposition. The insulator is held in its seat in the shell by anysuitable means such as by annular C-shaped spring 16, metal washer 18and the upper part 20 of the shell which is threaded in the lower part10 and may also be welded or brazed thereto. tween the shoulders of theinsulator 14 and the shell 10 and C-shaped spring 16 to distribute thepressure evenly on the insulator. The upper portion 20 of the shell isprovided with the usual sleeve 22 of insulating material held in placeby any suitable means. Insulator 14 is provided with a central bore 24having an enlarged upper end and a reduced lower end. Fitted within thereduced lower end is the lower electrode section 26 which may be made ofmetal, such as nickel, which is resistant to heat as well as to sparkerosion. This portion of the electrode has an enlarged upper end whichseats on the shoulder formed at the junction of the enlarged and reducedportions of the insulator bore 24, and is preferably of hollowconstruction with the center lled with metal such as copper, indicatedat 28, having good heat conductivity.

Above the lower electrode section is the conducting glass seal 30; abovethat a resistance element 32; and

Suitable gaskets are interposed bev 2,717,438 g Patented Sept.13, 1,955

above the resistance.` element `a second conducting p glass seal 34 orrwhich"isiseated;the disca421 ofthe lower ele'c-` trode 44 ofthe'auxiliary gap;v An'additional 'glass seal 31"'- engages` and 'grips vthe-lower threaded Ylor serratedgend 'of the upper electrode ele`u1entf38.VY Y The auxiliary 'spark gap assemblyj 36 'is of' simple con-V structionconsisting ofr a sleeve' y41)*"of insulatingfmateriahi, preferablysteatte, althouglraluminumj 'oxide'for otherV cef; rarnic compositions"maybeemployed. St'eatite vis .preferf able' because it 'maybeY readily.'cut 'to' the,.'desired'.`size`. Theersleeve shouldjhave' a'.roughj"surfa'ce to .reducethe possibility 'of 'shortfcircuiting by rdepositionof the -metal sputtered fromthe electrode." ,Eachend of'tliecylfinder.,is closed by adisc `42l 1avingsecured, centrallylth'eretoacylindricalelectrodeisection The dises 42preferably, consist of heatresistant conducting material; such as Vcom-l mercial nickel, and theelectrodes 44arekpreferablylmade" of 'tungsten because of. Aitsexcellent resistance to' heat, spark'erosion and oxidation.V'Ilietungstencontacts may., be secured tother nickel discs bywcopperbr`azing0r..the like. Other Amaterials "suitable for use,l aselectrode'saal!" thoughinefe'rior to.tungsten.are'platinum, platinumtung?, sten alloy, `nickel andl other allo'ysA commonly; used "fon sparkfplugeleetrode's. Copper-will" be found .`satisfac tory T where `lowerfabricating andf'operating ,temperatures are involved.'` y Y lThe-.auxiliary v'spark 'gap ,should be.of 'suchlength that. the voltageacross itis substantially the same as thatfacross., the gap of the plug.Asthe `pressure anthesauxili'ary gap is` .atmospheric ,and Imuch lowerthan inl.the combustion chamber the auxiliary gap Idistance should bemuchgreat-- er than the sparkg'glP-.- I

The conductinglgla'ss sealsl. and 34 fand 'the resistancev element. 32"may be; of 'the constructio'n described and 'claimed .in` the p rfiorAapplication of.,'McDougaLlA Schwartzwalde'r and Rulk,.SerialNol-,488',114,le'd May., 24, 219431 Thus `the seals' 30 .and'34 maybeniadekoflfznA fused mixture.` ofi55fparts, powderedy copper, 45. Pyrexor borosilicateI glass together with 3 `parts of a suitable bindersuch'as Dritex, a hydrogenated cottonseed oil.

The resistor 32 may be made of a mixture of 62.4% borosilicate glass(Pyrex cullet), 25.2% fluorspar (CaFn), 7.8% magnesium borosilicateglass and 4.6% Thermax carbon, a form of carbon black.

The glass Seal 37 above the spark gap may consist of Pyrex glass but thefollowing composition is preferred:

It will be noted that this seal contains no organic binder correspondingto the Dritex used in the conducting glass seals 30 and 34. It has beenfound that when a binder is present in the glass seal compositionsduring the fusing of the glass in the insulator bore a carbon film isdeposited on the insulating sleeve 40 of the spark gap, which lowers theinsulation resistance of the auxiliary spark gap assembly and may causethe gap to.be inoperative. However, when the binder is omitted thepowdered material is diicult to handle in the small amounts required.Consequently instead of omitting a binder entirely from the compositionof the conducting glass seals 30 and 34, the binder is employed to formthe powdered material into pellets which are subsequently sintered,preferably in a hydrogen atmosphere, at from 1500 to 1700 F. for fromfifteen minutes to one hour. The resulting pellets are substantiallyfree from the binder and may be readily handled in manufacture.

In assembling the electrode in the insulator the lower electrode element28 is inserted in the bore followed by the powdered or pelletedmaterials constituting the lower conducting glass seal 30; then bythepulverized or pelleted material forming the resistor 32 and then by thepulverized or pelleted material forming the upper conducting glass seal34. It has been found best to use either all powdered material or allpelleted material for the parts 30-32-34 as the combination of powderedand pelleted material does not produce the desired nal structure.Thereafter the spark gap assembly, the glass seal 37 and the upperelectrode section 38 are inserted and the assembly is then heated to asuiiicient temperature to soften the glass of the seals and resistanceelement whereupon the upper electrode section 38 is pressed down tocause it to seat on the upper disc 42 and make a tight assembly. Onsolidication the conducting glass seals 30 and 34 form an air-tightunion with the Walls of the bore in the insulator and grip the otherparts with which they make Contact.

An important feature of the invention is the character of the glass seal37. It has been found that when a gastight seal is used at this locationthe voltage across the auxiliary spark gap increases as the plug is usedbecause of disappearance of the air from the gap. The preferred glasscomposition of the seal 37 produces a crazed or finely cracked glasswhich, while securely united to the insulator and the cooperating parts,nevertheless permits seepage of air into 4the auxiliary gap. With thisconstruction the voltage drop across the auxiliary gap has remainedsubstantially constant throughout the life of the plug.

In the modification shown in Figure 2 the construction of the shell andthe manner of mounting the insulator in the shell is substantially thesame as that previously described. The electrode, however, consists of aplatinum tip ,50, the upper end of which is slightly enlarged and restson a shoulder provided in the bottom of the bore 52 in the insulator.The section 54 of the electrode consists of silver cast in place. Abovethe silver is the glass seal 56 which may be of the copper glasslcomposition described with the Dritex eliminated by baking the glasspellets. If desired, a resistance may be incorporated in the glass sealas disclosed in Figure l. upper section of the electrode, the lower endof which rests on the upper disc of the auxiliary gap assembly indicatedat 60. The electrode section 58 may be corrugated or grooved as in thepreceding form to better interlock with the glass of the seal 57 whichis of the same composition as the seal 37 of Figure l.

Various modifications will occur to those skilled in thev art. Thus, forexample, compressed powdered talc lcould be used in place of the glassseals, suitable means being provided to hold it under compression. Theupper seal instead of consisting of crazed glass permitting theentranceof air could be provided with a vent for the same purpose.

Various other modifications will occur to those skilled in the art.

We claim: Y

The method of making spark plugs having an auxiliary gap therein, saidmethod comprising the steps of preparing a ired ceramic insulator with acentral bore, arranging therein in the order named, a lower electrodesection, a powdered mixture of glass and electrically conducting heatresistant material, an auxiliary gap assembly comprising a lowerelectrode, an upper electrode and-aY tubular insulator interposedtherebetween, a quantity of powdered glass adapted after softening andcooling to form a crazed or cracked structure pervious to air and anupper electrode section, heating the assembly to soften the glass,applying pressure axially to said upper electrode section to cause it toseat in electrically circuit engaging relationship on the upperelectrode of the auxiliary gap while simultaneously causing theotherparts of the Velectrode to form a tight assembly and thereaftercooling the assembly to cause the glass to solidify in situ withtheglass surrounding said upper electrode section crazing to admit air tosaid auxiliary gap assembly.

References Cited in the file of this patent UNITED STATES PATENTS-2,371,2l1 Barrington Mar. 13, 1945 2,453,048 Tognola et al Nov. 2, 194858 Vindicatesv the

